Wireless monitoring is becoming more and more important in various applications, such as in industrial process automation systems and asset monitoring and control systems. In these types of monitoring applications, wireless sensors can be used to measure physical, chemical, or other parameters in inaccessible, hazardous, or other areas. Example aspects that can be monitored include the force, pressure, or torque of a rotating shaft, the temperature of moving or rotating parts, or the identification of marks on products or other objects. Among other things, wireless sensors could be used to support real-time control of an industrial process.
Many conventional wireless sensing applications are based on the use of battery-powered sensors, which increase the size and weight of the sensors. For large sensor networks, power management operations related to on-time battery replacement are often a costly and time-consuming task. As a result, wireless sensors that operate without batteries are emerging for real-time process control and other applications.